Zero thermal expansion material and practical component parts making use of the same

ABSTRACT

Using as a negative thermal expansion material a double oxide containing at least partly a compound represented by the chemical formula: RQ 2 O 8  (wherein R is Zr, Hf or a tetravalent metallic element represented by a mixture system of these, and Q is a hexavalent metallic element selected from W and Mo), and using as a positive thermal expansion material a material containing at least partly a compound represented by the chemical formula: MQX 4  (wherein M is Mg, Ca, Sr, Ba, Ra or a divalent metallic element represented by a mixture system of any of these, Q is a hexavalent metallic element selected from W and Mo, and X is an element selected from O and S), these are mixed preferably in a weight ratio of 1:1 and are synthesized to obtain a material whose coefficient of thermal expansion is substantially zero over a wide temperature range, i.e., a zero thermal expansion material. Using this zero thermal expansion material, high-precision and high-performance practical component parts can be obtained.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a zero thermal expansion material and apractical component part making use of the same, which are used inelectronic materials, precision machine component parts, structuralmaterials and so forth of products making use of high frequencies.

[0003] 2. Description of the Prior Art

[0004] Electronic materials and structural materials have conventionallybeen produced using oxides and resins or using glass and metals. Forexample, substrates for high-frequency circuits have been produced usingdielectrics or resins which have been made into sheets or plates. Suchconventional electronic materials and structural materials usually havepositive coefficients of thermal expansion. Hence, these materials haveproperties of causing expansion and contraction in accordance with riseand drop of ambient temperature.

[0005] Meanwhile, in recent years, materials whose coefficients ofthermal expansion are negative in some crystal systems are reported. Forexample, in Chemi. Mater., 1995, 7, 412-417, K. Korthuis et al. reportsZrV₂O₇. In Chemi. Mater., 8, 1996, 2809-2823, J. S. O. Evans et al.reports ZrW₂O₈ and HfW₂O₈. In Pysica B 241-243(1998) 311-316, the sameJ. S. O. Evans et al. reports materials having the general formula:A₂(MO₄)₃ (A is Al, Y or a lanthanum group element), in particular,materials wherein A is Sc. In Journal of Solid-State Chemistry, 149,92-98 (2000), D. A. Woodcock et al. also reports materials having thegeneral formula: A₂(MO₄)₃) (A is Al, Y or a lanthanum group element), inparticular, materials wherein A is Y or Al.

[0006] Of these, Evans et al. asserts negative thermal expansion theorythat, in materials having negative coefficients of thermal expansion,the whole bonding distance contracts because rotary motion increaseswith a rise in temperature, in an M—O—M (M is a metallic element) bond.

[0007] As these reports have been made, it has been studied tomaterialize a material having a low absolute value of coefficient ofthermal expansion (a low thermal expansion material), using a mixture ofa material having a positive coefficient of thermal expansion and thematerial having a negative coefficient of thermal expansion as in theforegoing. For example, Sleight et al.'s U.S. Pat. Nos. 5,322,559 and5,433,778 disclose low thermal expansion materials comprised of acomposite material of the above negative thermal expansion material andan epoxy resin.

[0008] However, it has not been reported that a method of producing sucha material is applied to ceramic materials used widely in, e.g.,high-frequency circuit component parts and the negative thermalexpansion material and a ceramic material are simultaneously fired toproduce a new low thermal expansion material.

[0009] Thus, conventional electronic materials or component parts andstructural materials, which have positive coefficients of thermalexpansion, inevitably cause expansion and contraction in accordance withchanges in ambient temperature. Even a slight error in size thus causedinevitably brings about a great lowering of performance in the case ofelectronic materials, precision machine component parts and so forthused in high-frequency circuit component parts. Hence, such materialshave had problems that not only any high working precision cannot beachieved but also electric and electronic properties tend todeteriorate.

[0010] More specifically, in such electronic materials or componentparts, precision machine component parts and structural materials, notonly a high working precision is required, but also, at the stage ofproduction, the coefficient of thermal expansion must be controlled inaccordance with use environment.

[0011] In addition, where materials free of any expansion andcontraction in a high-temperature condition are demanded, there has beena problem that the composite material comprised of an epoxy resin and anegative thermal expansion material as reported by Sleight et al. cannot substantially materialize such materials.

[0012] More specifically, in the field of precision machines in whichthe working precision is required in the order of microns, the abovecomposite material can not cope with its use in a high-temperaturecondition. Accordingly, it is sought to provide structural materials andprecision machine component parts making use of a material substantiallyfree of any expansion and contraction over a wide temperature range.

SUMMARY OF THE INVENTION

[0013] An object of the present invention is to provide a material whosecoefficient of thermal expansion is substantially zero over a widetemperature range (a zero thermal expansion material), and also toprovide various materials and component parts making use of thismaterials and having good properties.

[0014] To achieve the above object, the present invention provides azero thermal expansion material comprising a mixed material of anegative thermal expansion material and a positive thermal expansionmaterial;

[0015] the negative thermal expansion material comprising a double oxidecontaining at least partly a compound represented by the chemicalformula: RQ₂O₈ (wherein R is Zr, Hf or a tetravalent metallic elementrepresented by a mixture system of these, and Q is a hexavalent metallicelement selected from W and Mo); and the positive thermal expansionmaterial comprising a material containing at least partly a compoundrepresented by the chemical formula: MQX₄ (wherein M is Mg, Ca, Sr, Ba,Ra or a divalent metallic element represented by a mixture system of anyof these, Q is a hexavalent metallic element selected from W and Mo, andX is an element selected from O and S).

[0016] The present invention also provides a zero thermal expansionmaterial comprising a double oxide represented by the chemical formula:(RM) (QO₄)₃ (wherein R is Zr, Hf or a tetravalent metallic elementrepresented by a mixture system of these, M is Mg, Ca, Sr, Ba, Ra or adivalent metallic element represented by a mixture system of any ofthese, and Q is a hexavalent metallic element selected from W and Mo).

[0017] The present invention enables production of a zero thermalexpansion material whose coefficient of thermal expansion issubstantially zero. Since a ceramic material is used as the positivethermal expansion material, the coefficient of thermal expansion maylittle change even at a high temperature of 1,000° C. or more. Thismakes it possible to provide a zero thermal expansion material which isa heat-resistant material also having a high working precision.

[0018] The present invention still also provides a practical componentpart making use of any of these zero thermal expansion materials, whichmore specifically includes high-frequency circuit substrates,high-frequency circuit component parts, precision machine componentparts and structural materials.

[0019] Thus, when high frequencies in the millimeter wave range are usedwhere, e.g., a component part has a length corresponding to wavelengthat most, it is possible to actually provide electronic materials havinga high-precision workability and also having a substantially zerocoefficient of thermal expansion, and high-performance electroniccomponent parts which may undergo less variations in characteristics dueto temperature. In the filed of precision machines for which workingprecision is required in the order of microns, it is possible to providegood structural material and precision machine component partssubstantially free of any expansion and contraction over a widetemperature range.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a graph of characteristics which shows coefficients ofthermal expansion of materials according to an embodiment of the presentinvention.

[0021]FIG. 2 is a graph of characteristics which shows X-ray diffractionpatterns of materials according to an embodiment of the presentinvention.

[0022]FIG. 3 is a graph of characteristics which shows X-ray diffractionpatterns of materials according to an embodiment of the presentinvention.

[0023]FIG. 4 is a perspective view showing a band-pass filter accordingto an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] In a first embodiment of the present invention, it is a zerothermal expansion material comprising a mixed material of a negativethermal expansion material and a positive thermal expansion material.The negative thermal expansion material comprises a double oxidecontaining at least partly a compound represented by the chemicalformula: RQ₂O₈ (wherein R is Zr, Hf or a tetravalent metallic elementrepresented by a mixture system of these, and Q is a hexavalent metallicelement selected from W and Mo). The positive thermal expansion materialcomprises a material containing at least partly a compound representedby the chemical formula: MQX₄ (where in M is Mg, Ca, Sr, Ba, Ra or adivalent metallic element represented by a mixture system of these, Q isa hexavalent metallic element selected from W and Mo, and X is anelement selected from O and S). This material has the action to enablecontrol of the coefficient of thermal expansion to substantially zero.

[0025] In a second embodiment of the present invention, it is a zerothermal expansion material comprising a double oxide represented by thechemical formula: (RM)(QO₄)₃ (wherein R is Zr, Hf or a tetravalentmetallic element represented by a mixture system of these, M is Mg, Ca,Sr, Ba, Ra or a divalent metallic element represented by a mixturesystem of any of these, and Q is a hexavalent metallic element selectedfrom W and Mo). This material has the action to enable control of thecoefficient of thermal expansion by controlling its content.

[0026] In the zero thermal expansion material according to the secondembodiment, it may preferably be a material in which R is Zr, Hf or atetravalent metallic element containing these, M is Mg and Q is ahexavalent metallic element selected from W and Mo. It may morepreferably be a zero thermal expansion material in which R is Hf, M isMg and Q is W.

[0027] The present invention is also a high-frequency circuit substratemaking use of any of the above zero thermal expansion materials, whichhas the action to make any shape change due to temperature less occurand to stabilize electrical properties in the millimeter wave range.

[0028] The present invention is still also a high-frequency circuitcomponent part making use of any of the above zero thermal expansionmaterials, which has the action to make any shape change due totemperature less occur and to stabilize electrical properties in themillimeter wave range.

[0029] The present invention is further a precision machine componentpart making use of any of the above zero thermal expansion materials,which has the action to lessen any scattering in working precision dueto temperature.

[0030] The present invention is still further a structural materialmaking use of any of the above zero thermal expansion materials, whichhas the action to lessen any scattering in working precision due totemperature.

[0031] Embodiments of the present invention are described below withreference to FIGS. 1 to 3.

EMBODIMENT 1

[0032] In this embodiment of the present invention, shown is a case inwhich a zero thermal expansion material is produced using a materialcontaining the double oxide represented by the chemical formula: (RM)(QO₄)₃ (wherein R is Zr, Hf or a tetravalent metallic elementrepresented by a mixture system of these, M is Mg, Ca, Sr, Ba, Ra or adivalent metallic element represented by a mixture system of these, andQ is a hexavalent metallic element selected from W and Mo). Materialsused are a material A [A is a material having a crystal system of RQ₂O₂,and having a coefficient of thermal expansion which is negative(coefficient of thermal expansion: α (α>0); density: a] and a material B[B is a material having a crystal system of MQO₄, and having acoefficient of thermal expansion which is positive (coefficient ofthermal expansion: β; density: b]. Coefficients of thermal expansion ofchief materials are shown in Table 1 below. TABLE 1 Dielectric constantCoefficient of Materials (room thermal expansion temperature) (×10⁻⁶/°C.) HfW₂O₈ 15˜20 −5˜−10 ZrW₂O₈ −8.3 SiO₂ 3.5˜4.6 +0.36 (quartz glass)Al₂O₃ 8.0˜11.0 +5˜6.7 MgO +10.4 Al₆Si₂O₁₃ +5.4 MgAl₂O₄ 7.6˜9.0 +8.8MgSiO₃ 6.0 (positive) MgSiO₄ 6.4 +10˜11 Mg₂Al₄Si₅O₁₈ +16˜63 MgWO₄ 18+5˜8 HfSiO₄ (positive) ZrSiO₄ +3.7

[0033] The materials A and B may be mixed in a volume ratio A:B of β:α,followed by firing to produce a material containing a double oxidehaving the crystal structure of (RM) (QO₄ )₃, where the coefficient ofthermal expansion comes to substantially zero.

[0034] Where the coefficient of thermal expansion and density ofmaterials are evident, the materials may be so weighed and mixed thatweights x and y of the materials A and B come to be x:y=aβ:bα (Equation1), followed by firing to produce the material containing a double oxidehaving the crystal structure of (RM) (QO₄)₃, where the coefficient ofthermal expansion comes to substantially zero.

[0035] Here, the double oxide having the crystal structure of(R²⁺M⁴⁺)(QO₄)₃ has the same structure as the negative thermal expansionmaterial A³⁺ ₂ (QO₄)₃ reported by Evans et al., and, as a result of itsX-ray diffraction, this oxide is considered to be a double oxide havingcrystal structure wherein the site of (A³⁺ ₂) has been substituted with(R²⁺M⁴⁺). More specifically, the substitution of (A³⁺ ₂) with (R²⁺M⁴⁺)is considered to be indispensable to materialize low thermal expansionmaterials, Also, these materials are expressed as (RO₂)(MO)(QO₃)₃ insome cases.

[0036] With regard to the mixing ratio, since characteristic values(such as coefficient of thermal expansion and density) of the positivematerial and negative material may vary depending on pretreatment suchas mixing and pulverization of materials, and on sintering conditionssuch as temperature of calcination, temperature of main-treatmentfiring, pressure and environment, care must be taken to mix them on thebasis of characteristic values of materials just before their mixing.

[0037] As a specific example, a zero thermal expansion materialcontaining (HfMg) (WO₄)₃, which is one of the double oxide (RM)(QO₄)₃,is described below in detail as an experimental report. This zerothermal expansion material may be produced using HfW₂O₈ and MgWO₄ as thematerial A and the material B, respectively.

[0038] As to the HfW₂O₈, HfO₂ (available from Kanto Kagaku K. K.;purity: 99.5%) and WO₃ (available from High Purity Chemicals Co., Ltd.;purity: 4N) were used as starting materials. These were so weighed thatHfO₂ and WO₃ came to be in a molar ratio of 1:2, and then mixed andpulverized by means of a ball mill. The raw-material powder thusobtained was calcined at 1,150° C. to produce HfW₂O₈.

[0039] Similarly, as to the MgWO₄, too, MgO and WO₃ were weighed in amolar ratio of 1:2, and then mixed and pulverized by means of a ballmill. The raw-material powder thus obtained was thereafter calcined at1,000° C. to produce MgWO₄.

[0040] The respective calcined powders were measured by X-raydiffraction to ascertain that the reaction had sufficiently proceeded.

[0041] Next, since the HfW₂O₈ had a coefficient of thermal expansion of−8 ppm/° C. and a theoretical density of 5.884 g/cm³ and the MgWO₄ had acoefficient of thermal expansion of +8 ppm/° C. and a theoreticaldensity of 5.77 g/cm³, having the size of coefficient of thermalexpansion and the density which were substantially equal to each other,the calcined powders of HfW₂O₈ and MgWO₄ were so weighed as to be in aweight ratio of 1:1 (M:H=1:1), and then mixed and pulverizedsufficiently by means of a ball mill, followed by extrusion intopellets. These pellets of the mixed powder were molded, followed bymain-treatment firing at 1,150° C., and the coefficient of thermalexpansion of the resultant molded product was measured. Results obtainedare shown in FIG. 1. As shown in FIG. 1 by a solid line, it was able toobtain a zero thermal expansion material whose coefficient of thermalexpansion was ±1×10⁻⁶/° C. or less in any temperature range of from roomtemperature to 1,000° C.

[0042] It was also able to synthesize a material having a coefficient ofthermal expansion of −4 ppm/° C. when HfW₂O₈ and MgWO₄ were mixed in aratio of 3:1 (M:H=1:3), and to synthesize a material having acoefficient of thermal expansion of +4 ppm/° C. when HfW₂O₈ and MgWO₄were mixed in a ratio of 3:1 (M:H=3:1). These results are also shown inFIG. 1 by chain lines. The coefficients of thermal expansion when HfW₂O₈and MgWO₄ were each used alone are also shown as references in FIG. 1 bydoted lines.

[0043] The materials showing the coefficients of thermal expansion shownin FIG. 1 were analyzed by X-ray diffraction to obtain the results shownin FIGS. 2 and 3 as X-ray diffraction patterns.

[0044]FIG. 2 shows three X-ray diffraction patterns of the HfW₂O₈, theMgWO₄ and the material prepared by mixing these in 1:1. As can be seentherefrom, in the material of 1:1 mixture, (HfMg)(WO₄)₃ has beensynthesized in addition to HfW₂O₈ and MgWO₄.

[0045]FIG. 3 shows three X-ray diffraction patterns of the materialprepared by mixing HfW₂O₈ and MgWO₄ in 1:1, the material prepared bymixing these in 1:3 and the material prepared by mixing these in 3:1. Ascan be seen therefrom, in the materials of 1:3 and 3:1 mixture, too,(HfMg)(WO₄)₃ has been synthesized like the material of 1:1 mixture.

[0046] Thus, as can clearly be seen from FIGS. 2 and 3, in order tosynthesize the zero thermal expansion material and control thecoefficient of thermal expansion, it is indispensable for the materialto contain the material having crystal structure such as the(HfMg)(WO₄)₃, i.e., the double oxide represented by the formula:(RM)(QO₄)₃.

[0047] As a different example, using ZrW₂O₈ or a mixture of HfW₂O₈ andZrW₂O₈, a zero thermal expansion material was produced adding MgWO₄thereto. In such a case, too, it was possible to obtain a zero thermalexpansion material whose coefficient of thermal expansion was similarly±2×10⁻⁶/° C. or less in the temperature range of from room temperatureto 1,000° C.

[0048] In the material of this example, synthesis of a materials of(ZrMg)(WO₄)₃ or (Zr_(x)Hf_(1-x)Mg)(WO₄)₃ has been ascertained. Thus, ascan also clearly be seen from this example, it is indispensable for thezero thermal expansion material of the present invention to contain thedouble oxide represented by the formula: (RM) (QO₄)₃.

EMBODIMENT 2

[0049]FIG. 4 is a perspective view showing a band-pass filter making useof the zero thermal expansion material, according to this Embodiment.

[0050] To the outset, using the calcined powders of HfW₂O₈ and MgWO₄weighed in a weight ratio of 1:1 as used in Embodiment 1, these weremixed together with a binder resin by means of a ball mill, and a greensheet was obtained from the resultant mixture by a doctor blade method.Then, the green sheet thus obtained was cut in a desired size, andtwenty cut sheets were so piled up as to be 1 mm in plate thicknessafter firing, followed by compression molding. The molded productobtained was fired at 1,150° C. to obtain a platelike sintered body fora high-frequency circuit substrate. The coefficient of thermal expansionof this plate was measured to find that it was +0.8 ppm/° C. Needless tosay, the plate produced here contained the material of (HfMg) (WO₄)₃.

[0051] Next, as shown in FIG. 4, this platelike sintered body was usedas a dielectric substrate 1 of a high-frequency circuit substrate. Onthis substrate, strip lines were formed using metal conductors 2 to makeup a band-pass filter.

[0052] Filter characteristics at room temperature up to 100° C. weremeasured. As the result, since the substrate had a small coefficient ofthermal expansion, a filter with stable frequency characteristics wasobtainable.

[0053] As described above, substrates and component parts having goodcharacteristics can be obtained by producing substrates forhigh-frequency circuits and component parts for high-frequency circuits,using the zero thermal expansion material having a small coefficient ofthermal expansion.

[0054] In the case when the HfW₂O₈ and MgWO₄ are thus used, the weightratio of these may be changed to control the content of (HfMg) (WO₄)₃.Such control makes it easy to control the coefficient of thermalexpansion arbitrarily between −8 ppm/° C. and +8 ppm/° C. over a widetemperature range of from room temperature to 1,000° C. Also, use ofdifferent materials enables change of the range of control of thecoefficient of thermal expansion to any desired range.

[0055] Thus, where the precision in the order of microns is required inrelation to surrounding members, as in the case of precision machinecomponent parts and structural materials, the present invention iseffective of course when the coefficient of thermal expansion is zeroand also when the coefficient of thermal expansion should be controlled.

[0056] As described above, according to the present invention, asuperior zero thermal expansion material whose coefficient of thermalexpansion is substantially zero can be provided. Also, the use of thismaterial brings about an advantageous effect that high-precision andhigh-performance practical component parts such as high-frequencycircuit substrates and high-frequency circuit component parts, precisionmachine component parts and structural materials can be provided.

1-9. (Canceled)
 10. A process for producing a zero thermal expansionmaterial; the process comprising mixing a negative thermal expansionmaterial and a positive thermal expansion material, followed by firing;said negative thermal expansion material comprising a double oxidecontaining at least partly a compound represented by the chemicalformula: RQ₂O₈ wherein R is Zr, Hf or a tetravalent metallic elementrepresented by a mixture system of these, and Q is a hexavalent metallicelement selected from W and Mo; and said positive thermal expansionmaterial comprising a material containing at least partly a compoundrepresented by the chemical formula: MQX₄ wherein M is Mg, Ca, Sr, Ba,Ra or a divalent metallic element represented by a mixture system of anyof these, Q is a hexavalent metallic element selected from W and Mo, andX is an element selected from O and S.
 11. The process for producing azero thermal expansion material according to claim 10, wherein said R isZr, Hf or a tetravalent metallic element containing these, said M beingMg.
 12. The process for producing a zero thermal expansion materialaccording to claim 10, wherein said R is Hf, M is Mg and Q Is W.
 13. Theprocess for producing a zero thermal expansion material according toclaim 10, wherein a weight ratio of RQ₂O₈ and MQX₄ is about 1:1.